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Nine Men's Morris is a duel of mills: line up three of your pieces along any marked line and you get to pluck one of your opponent's pieces off the board. The catch is that the game changes character three times. First you both drop your nine pieces onto the 24 intersections, fighting for the well-connected crossings where two mills meet. Then you grind through the movement phase, sliding along the lines to open and re-close mills. Finally, when someone is whittled down to three pieces, those survivors gain the power to "fly" anywhere, turning a losing position into a knife-fight. Outlast your rival to two pieces, or freeze them with no legal move, and the win is yours.
How to Play Nine Men's Morris
The board is three concentric squares joined by lines at the midpoints of their sides, giving 24 intersection points. Each player gets nine pieces. In the placement phase you take turns dropping one piece on any empty intersection until all 18 pieces are down. Whenever you complete a mill — three of your own pieces on one of the board's straight lines — you immediately remove one of the opponent's pieces. Only orthogonal lines count as mills here; there are no diagonal mills, so the board has exactly 16 mills (eight horizontal, eight vertical).
Once every piece is placed, the movement phase begins: on your turn you slide one piece along a line to an adjacent empty point. You cannot jump over pieces or hop to a non-connected point. Forming a fresh mill on the move again lets you capture one enemy piece. When you remove a piece you must take one that is NOT currently part of a mill, unless every opponent piece is locked inside a mill — only then may you take one from a mill.
When a player is reduced to exactly three pieces, those pieces enter the flying phase and may move to any empty intersection regardless of adjacency. You win in one of two ways: reduce the opponent to two pieces (they can no longer form a mill), or leave them with no legal move on their turn. Once all pieces are placed, 50 moves in a row (counting both players) without a capture end the game in a draw. The reduce-to-two win is only triggered once the player being reduced has finished placing all nine of their pieces, so captures during the early placement phase never end the game outright.
Playing Against the Computer
The computer searches ahead with minimax, including when it chooses which piece to capture after a mill. Its evaluation rewards pieces, completed mills, 'two-of-three' lines with the third point empty, and mobility, and it recognizes a win by capture or by blocking when it falls within its search. Easy searches two moves deep (counting each player's move) and picks at random among its four best moves, Medium searches four moves deep and picks between its two best, and Hard searches up to ten moves deep, thinks the longest, and always plays the best move it finds. Even Easy and Medium take a win they can see and avoid a move they see losing. Against Hard you need clean double threats; against the lower levels, patient mill-building will punish their occasional slips.
Frequently Asked Questions
Are there diagonal mills in this version of Nine Men's Morris?
No. This version uses only the 16 straight lines along the squares' sides — eight horizontal and eight vertical. Three pieces on a diagonal do not form a mill and do not let you capture. This matches the traditional ruleset; the diagonal-mill variant is a different game.
Can I capture an opponent's piece that is already inside a mill?
Normally no. When you complete a mill you must remove a piece that is NOT part of any of the opponent's mills. The only exception is when every one of the opponent's pieces sits inside a mill — then, and only then, you may remove one from a mill.
What is the 'flying' phase and when does it start?
When a player is reduced to exactly three pieces, those pieces gain the ability to fly: instead of sliding to an adjacent point, they may jump to any empty intersection on the board. It kicks in automatically at three pieces and gives the trailing player a real chance to fight back by reaching any threatened mill in one move.
Can captures during the placement phase win the game immediately?
No. You can form mills and remove enemy pieces while placing, but the 'reduced to two pieces' loss is only checked once the player being reduced has finished placing all nine of their pieces. So losing pieces early in placement never ends the game on the spot — play continues until that condition (or a no-legal-move position) is reached after placement is done.
Are all 24 points equally valuable, and can the game end in a draw?
Every point lies on exactly two mills, so no point belongs to 'more lines' than another — but the four midpoints of the middle square, where the connecting lines cross, have four connections (corners have two, the other midpoints three), giving far more mobility and serving as swing-mill hubs, which makes them the most valuable squares. As for draws: once all pieces are placed, 50 moves in a row (counting both players) without a capture end the game in a draw. Otherwise it resolves to a win — either someone is reduced below three pieces (after placing all nine) or someone is left with no legal move.